Description:

Objective:

Activated carbon is commonly used to remove high explosives such as RDX from groundwater, but the safe handling of spent carbon granules is both hazardous and costly. Therefore, this work aims to develop a biological-chemical model system for adsorbed RDX transformation to granular activated carbon (GAC) using known electron-shuttle reducing microorganisms. Studies will utilize different cellular cultures to determine the rate and extent to which adsorbed RDX can be reduced using hydroquinone electron shuttles and will identify key intermediates in the degradation pathway.

Synopsis:

Explosives are a common groundwater contaminant at military facilities. Activated carbon is the most utilized treatment method; however, this produces explosive hazardous waste that is expensive to handle and dispose. This study aims to transform explosives on spent activated carbon, making the treated carbon nonhazardous and recyclable. Carbon will be treated using a combination of bacterial cultures and chemical additives. The project would enhance, not replace, current cleanup systems.

Approach:

Chemically reduced hydroquinones will be added to solutions containing RDX sorbed to GAC granules, and both GAC granules and aqueous solution will be analyzed for RDX and transformation products in order to determine whether hydroquinones can donate electrons to sorbed RDX as a one-way reaction. Next, GAC/RDX/quinone solutions will be inoculated with quinone-respiring Geobacter metallireducens to determine whether quinones could be reduced using cellular cultures, thus producing a continuous flow of electrons to RDX. Studies will progress to flow-through column experiments that mimic an ex-situ remedial system, and alternate cultures will be tested.

Expected Results:

Preliminary data suggest that chemically reduced hydroquinones can successfully transform RDX sorbed to activated carbon, although kinetics and extent of degradation are unknown. However, this reaction occurs in less than 48 hours, suggesting that sorbed RDX can be treated in a timely manner. Published studies have already proven that G. metallireducens can reduce quinones in aqueous solution; therefore, it is believed that the combination of cells and hydroquinones will produce a system where RDX is continuously reduced and GAC granules can be utilized indefinitely. It is believed that this cellular-chemical system can be retrofitted to existing GAC units that are already treating RDX.

Potential to Further Environmental/Human Health Protection:

The safe transport and landfilling of RDX-spent GAC requires a considerable amount of labor and cost; potentially explosive hazardous waste must be handled carefully and deliberately, and appropriate landfills are often far from clean-up sites. The proposed treatment strategy would reduce the risk of explosion and would eliminate the need for GAC landfilling as carbon granules will be continuously recycled.

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.